Multi-jet ink printer

ABSTRACT

An ink printer system in which line thickness and line separation are regulated by disposing a plurality of ink nozzles in a converging array and limiting undesirable electrostatic attraction forces active in the system. In one embodiment, an electrode is positioned between each adjacent pair of nozzles of the array with the electrodes being connected to a d.c. source having a value less than the peak value of the voltage pulses applied to the nozzles. In a second embodiment, alternate nozzles of the array receive video pulses of the opposite polarity whereby jets of ink drops having opposite charges are formed by adjacent nozzles of the array.

[ Nov. 12, 1974 1 MULTI-JET INK PRINTER [75] Inventors: John F. Mahoney, South Pasadena;

Julius Perel, Altadena, both of Calif.

[73] Assignee: Xerox Corporation, Stamford,

Conn.'

[22] Filed: Aug. 30, 1973 [21] Appl. No.: 392,913

[52] US. Cl 346/140, 118/625, 118/638, 346/75 [51] Int. Cl. G01d 15/18 [58] Field of Search 346/140, 75; 118/621, 623, 118/625, 629, 638; 317/3 [56] References Cited UNITED STATES PATENTS 3,052,213 9/1962 Schaffert 118/637 3,341,859 9/1967 Adams 346/140 3,446,183 5/1969 Drum 118/629 Primary Examiner-Joseph W. Hartary [57] ABSTRACT An ink printer system in which line thickness and line separation are regulated by disposing a plurality of ink nozzles in a converging array and limiting undesirable electrostatic attraction forces active in the system. In one embodiment, an electrode is positioned between each adjacent pair of nozzles of the array with the electrodes being connected to a dc. source having a value less than the peak value of the voltage pulses applied to the nozzles. In a second embodiment, alternate nozzles of the array receive video pulses of the opposite polarity whereby jets of ink drops having opposite charges are formed by adjacent nozzles of the array.

7 Claims, 3 Drawing Figures s e NAL SOURCE PATENTEL 8M 20$ 2 3.848.258

D. C. J32 SIGNAL SOURCE INVERTER MULTI-JET INK PRINTER BACKGROUND OF THE INVENTION Prior art devices for recording with liquid ink are generally of three basic types. The first type operates with physical contact between an ink-fed stylus and a recording surface with the stylus being physically removable from the recording surface on receipt of an appropriate signal. Drawbacks of this system include .difficulty associated with physical removal of the stylus under varying conditions of operation. At high operating speeds, such as is associated with a fast flow of intelligence, a highly damped, relatively non-elastic mechanical system is required which becomes impractical or impossible to construct.

A second of the prior existing types for liquid ink recording devices is one in which an ink-fed stylus is maintained in constant contact against a recording surface and is moved relative thereto in order to record inform ation, Like the last mentioned type, this provides a continuous mark onthe recording surface at all times when the stylus and recording surface are in contact. This type has been largely limited in practical applications to oscillograph use since mechanical complexity has been regarded as too prohibitive to control a continuously marking stylus for the tortuous configurations necessary for modern, sophisticated writing.

The last of the aforementioned types is referred to as ink spitters and includes devices in which ink is projected across a gap from'a nozzle point to a recording medium. One type of ink spitter is known as a continuous flow system in which ink drops are formed continuously in response to pressure and vibration. In the region adjacent to the nozzle there is placed a charging tunnel through which the ink drops are projected and which serves the function of applying charge to selected ink drops in accordance with a desired video signal to be produced. Downstream of the tunnel there is provided a set of deflecting plates which have a potential difference between them. The electric field which is created between the plates acts on the charged drops causing them to be deflected in an amount determined by the amplitude of the applied potential difference. Downstream of the deflection plates, a trough is provided for catching drops which do not have any charge and transferring them to a waste reservoir. There is provided also a writing medium which receives the deflected ink drops, whereby an image representative of I the video signals is produced. The writing medium is usually moved in synchronism with the application of the video signals to the drops. In addition to requiring an ink waste reservoir and possibly pumping means for transferring ink from the reservoir to the nozzle, with the inherent possibilities of ink spillage and failure of mechanical parts with such a system, the continuous flow ink spitters may not provide fidelity with the video signal. Obviously, if the video signal is in the process of rising or falling, or is not present at the time the drops separate, the charge on the drops will not be indicative of the video signal. In order to place separate charges on given drops, one must know when drop separation is occuring or the phasing of the drop formation relative to the video signal. In the absence of control of drop separation time, because of unpredictable phase changes in the ink drop formation, the uniformity and the fidelity of the printing are effected adversely.

A second type of ink spitter is known as an ondemand system in which ink drops are formed selectively in accordance with the video signal, all ink drops formed impinge on the recording medium. Such systems are described in U.S. Pat. Nos. 3,341,859 and 2,143,376. In these systems a conductive bar is placed behind the writing medium with a voltage of one polarity applied to the bar that is insufficient to draw ink from the nozzle. When it is desired to print, square wave or rectangular wave voltage pulses of the other polarity are selectively applied to the nozzle, and the paper is moved. The resulting electrostatic field between the nozzle and the bar will overcome the liquid surface tension and draw ink from the nozzle to the writing medium.

The desirability of an ink system that uses all ink drops for printing is apparent, that is, no ink drop deflection or ink recirculation is required. However, it is often desirable to provide greater ink line thickness than can be produced with a single nozzle. For this purpose it has been found convenient to arrange a plurality of ink nozzles or jets in a converging array (see U.S. Pat. No. 3,373,437). Such an arrangement of jets permits greater spacing between the individual jets than jets arranged in parallel. In such systems, where ink drops are'formed by an array of jets, voltage pulses of one polarity are applied simultaneously to selected nozzles and hence a plurality of jets of ink drops having the same charge are produced.

Since the jets of ink drops produced by a converging array of nozzles are of the same polarity, the electrostatic forces on the ink drops near the nozzles causes the jets to diverge while moving toward the writing medium. This repulsion results in an undesirable widening of the line thickness and, in some cases, variable line thicknesses. Furthermore, the electrostatic repulsion makes it difficult to provide two ink lines with a fixed spacing therebetween.

It is therefore an object of the present invention to provide an improved on-demand ink printing system.

It is a further object of the present invention to provide an improved on-demand ink printing system having an array of nozzles that can produce ink lines of controlled thickness.

It is a further object of the present invention to provide an improved on-demand ink printing system having a plurality of nozzles in a converging array.

In accordance with the invention, an ink printing system is provided in which line thickness and line separation are regulated by disposing a plurality of ink nozzles in a converging array and limiting undesirable electrostatic attraction forces acting on the jets of charged ink drops emanating from the nozzles. In one embodiment, an electrode is positioned between each adjacent pair of nozzles of the array with the electrodes being connected to a dc. source having a value less than the peak value of the voltage pulses applied to the nozzles. The

polarity of the dc. source is generally the same as that of the voltage pulses applied to the nozzles. In a second embodiment, alternate nozzles of the array receive video pulses of the opposite polarity whereby jets of ink drops having opposite charges are formed by adjacent nozzles of the array. With both embodiments undesirable electrostatic interaction forces active in the system are limited, thereby allowing the jets of inkdrops to follow a substantially straight-line path from the nozzles to a selected area of the recording medium.

The novel features of the invention are set forth in particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of one embodiment of the ink printing system in accordance with the present invention.

FIG. 2 shows a waveform that can be supplied to the nozzles of the ink printing systems of FIGS. 1 and 3.

FIG. 3 is a second embodiment of an ink printing system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT only about 1 cm of water, the capillary forces at the capillary tips are not overcome, and hence ink does not normally flow from the nozzles 10, 12, and 14. Instead, a convex meniscus forms on the tips of the nozzles. A flow in the form of ink drops of very small cross section is produced only when the meniscus is subjected to the action of an electrostatic field of a certain value. The

inner diameter of the tips 11, 13, and 15 can be rather large, for example, 0.15mm, since the pressure is low. The outer diameter of the tips 11, 13, and 15 controls the size of the meniscus, and is of the order of 0.25mm. Nozzles 10, 12, and 14 are positioned in a converging array such that ink drops emanating therefrom are projected toward a common area 22 of a recording medium 24 which passes over a platen 26 which is preferably at ground potential. While it is presently contemplated that the preferred form of the invention would include a circular array of nozzles with uniform spacing between nozzles, it will be appreciated that such uniform spatial relationship of the nozzles is not essential.

If the voltage pulses to each nozzle have the same polarity, the ink drops of the jets flowing from the nozzles will have that polarity, that is, if a positive going voltage pulse is supplied to the nozzles 10, 12, and 14, the ink drops of the jets flowing from the nozzles will have a positive charge. As the newly formed charged ink drops leave the nozzles, the electrostatic interaction forces active in the 'vicinity of the nozzles causes the trajecto-' 22, each nozzle producing one line, the electrostatic forces on the jets of ink drops may cause the line spacing to increase or vary sporadically.

To overcome the electrostatic interaction forces active in the vicinity of the nozzles 10, 12, and 14, an electrode 28 is provided between nozzles 10 and 12 and an electrode 30 is provided between nozzles 12 and 14. Electrodes'28 and 30 have a dc. signal supplied thereto which signal has a value between the maximum value of the pulses supplied to the nozzles and the potential of platen 26. For example, if the voltage pulses supplied to nozzles 10, 12, and 14, by source 32 have a maximum positive value of 3-3.5 kilovolts with respect to ground, and the platen 26 is grounded, the dc. signal supplied to electrodes 28 and 30 would have a positive value of between 2-2.5 kilovolts with respect to ground. If the platen 26 was at a negative potential with respect to ground, the value of the signals applied to the nozzles and the electrodes 28 and 30 could be reduced and, if the negative potential on platen 26 had a sufficient value, the signal applied to electrodes 28 and 30 may beof the opposite polarity as the signal applied to the nozzles. The intermediate electrodes 28 and 30 control electrostatic interaction between adjacent nozzles, and hence control electrostatic forces on newly formed ink drops with the result that the trajectories of the ink drops from the different nozzles do not diverge.

FIG; 2 depicts the pulses of a waveform 40 illustrative of the signal supplied by source 32, each pulse producing desirably several ink drops. As shown, each pulse has a rapidly rising leading edge 42 which increases to a predetermined level 44 of, for example, 3500 volts with the nozzles and ink specifically men tioned previously, and is maintained at level 44 for a brief period, microseconds being appropriate. Preferably, the trailing edge 45 of each pulse decreases slowly either linearly or exponentially, as shown, to about base level 43.

FIG. is illustrative of another embodiment of the invention in which divergence of the trajectories of jets of ink drops from different nozzles of any array is controlled without intermediate electrodes. In this embodiment, in which components corresponding to like components of FIG. 1 have the same reference numbers, the waveform supplied to the intermediate nozzle 12 is of the polarity opposite to the polarity of the waveforms supplied to nozzles 10 and 14. As shown, this can be achieved by means of a conventional inverter circuit 46 disposed in the circuit supplying nozzle 12. With this system, the ink drops from nozzles 10 and 14, for example, have a positive polarity, and the ink drops from nozzle 12 have a negative polarity. Since the ink drops of the jet from middle nozzle 12 are of the polarity opposite to those ink drops from the outer nozzles 10 and 14, repulsion forces between the outer jets is pre-.

ably about 0.060 inches from areas 22 of recording medium 24.

While the invention has been described with reference to preferred embodiments thereof, it will be apparent to those skilled in the art that various changes may be made without departing from the true spirit and scope of the invention as set forth in the appended claims.

What is claimed is: l. A fluid printer for writing on a record medium comprising:

an array of a plurality of fluid-containing nozzles each having a capillary tip, the array being oriented such that a projection of the longitudinal axes of said nozzles converge toward an area of said record medium, first means for maintaining the voltage of said record medium at a reference value, second means for selectively supplying voltage pulses of the same polarity to the fluid contained in said nozzles, said voltage pulses having a peak value different from said reference value, an electrode disposed between adjacent pairs of said nozzles in the vicinity of said capillary tips of said nozzles, and third means for applying to said electrodes a voltage intermediate said peak value and said reference value thereby to allow fluid drops from said capillary tips to converge toward said area of said record medium even though the drops have the same polarity due to voltage pulses of the same polarity being applied to the fluid contained in said nozzles.

2. The printer of claim 1 wherein said nozzles are offset to each other at an angle of between and 30 degrees.

3. The printer of claim 2 wherein said peak value of said voltage pulses is in the range of 3,000 to 3,500 volts and said intermediate voltage has a value in the range of 2,000 to 2,500 volts.

4. A fluid printer for writing on a record medium comprising:

an array of a plurality of fluid-containing nozzles each having a capillary tip, the array being oriented such that a projection of the longitudinal axes of said nozzles converge toward an area of said record medium,

first means for maintaining the voltage of said record medium at a reference value,

second means for supplying voltage pulses of opposite polarity to the fluid contained in adjacent of said nozzles to thereby reduce undesirable electrostatic forces between fluid drops issuing from the capillary tips of adjacent nozzles. 5. The printer of claim 4 wherein said nozzles are offset to each other at an angle of between 15 and 30.

6. A fluid printer for writing on a record medium comprising:

an array of a plurality of fluid-containing nozzles each having a capillary tip, the nozzles of the array being offset to each other at an angle of between 15 and 30 and being oriented such that a projection of the longitudinal axes of said nozzles converge toward an area of said record medium,

first means for maintaining the voltage of said record medium at a reference value,

second means for selectively supplying voltage pulses of the same polarity to the fluid contained in each of said nozzles, said voltage pulses having a peak value different from said reference value,

an electrode disposed between adjacent pairs of said nozzles in the vicinity of the capillary tips of said nozzles, and

third means for supplying to said electrodes a potential having a value between said peak value and said reference value thereby to allow fluid drops from said capillary tips to converge toward said area of said record medium even though the drops have the same polarity due to voltage pulses of the same polarity being applied to the fluid contained in said nozzles.

7. A fluid printer for writing on a record medium comprising:

an array of a plurality of fluid-containing nozzles each having a capillary tip, the nozzles of the array 

1. A fluid printer for writing on a record medium comprising: an array of a plurality of fluid-containing nozzles each having a capillary tip, the array being oriented such that a projection of the longitudinal axes of said nozzles converge toward an area of said record medium, first means for maintaining the voltage of said record medium at a reference value, second means for selectively supplying voltage pulses of the same polarity to the fluid contained in said nozzles, said voltage pulses having a peak value different from said reference value, an electrode disposed between adjacent pairs of said nozzles in the vicinity of said capillary tips of said nozzles, and third means for applying to said electrodes a voltage intermediate said peak value and said reference value thereby to allow fluid Drops from said capillary tips to converge toward said area of said record medium even though the drops have the same polarity due to voltage pulses of the same polarity being applied to the fluid contained in said nozzles.
 2. The printer of claim 1 wherein said nozzles are offset to each other at an angle of between 15 and 30 degrees.
 3. The printer of claim 2 wherein said peak value of said voltage pulses is in the range of 3,000 to 3,500 volts and said intermediate voltage has a value in the range of 2,000 to 2,500 volts.
 4. A fluid printer for writing on a record medium comprising: an array of a plurality of fluid-containing nozzles each having a capillary tip, the array being oriented such that a projection of the longitudinal axes of said nozzles converge toward an area of said record medium, first means for maintaining the voltage of said record medium at a reference value, second means for supplying voltage pulses of opposite polarity to the fluid contained in adjacent of said nozzles to thereby reduce undesirable electrostatic forces between fluid drops issuing from the capillary tips of adjacent nozzles.
 5. The printer of claim 4 wherein said nozzles are offset to each other at an angle of between 15* and 30*.
 6. A fluid printer for writing on a record medium comprising: an array of a plurality of fluid-containing nozzles each having a capillary tip, the nozzles of the array being offset to each other at an angle of between 15* and 30* and being oriented such that a projection of the longitudinal axes of said nozzles converge toward an area of said record medium, first means for maintaining the voltage of said record medium at a reference value, second means for selectively supplying voltage pulses of the same polarity to the fluid contained in each of said nozzles, said voltage pulses having a peak value different from said reference value, an electrode disposed between adjacent pairs of said nozzles in the vicinity of the capillary tips of said nozzles, and third means for supplying to said electrodes a potential having a value between said peak value and said reference value thereby to allow fluid drops from said capillary tips to converge toward said area of said record medium even though the drops have the same polarity due to voltage pulses of the same polarity being applied to the fluid contained in said nozzles.
 7. A fluid printer for writing on a record medium comprising: an array of a plurality of fluid-containing nozzles each having a capillary tip, the nozzles of the array being offset to each other at an angle of between 15* and 30* with the array being oriented such that a projection of the longitudinal axes of said nozzles converge toward a common area of said record medium, first means for maintaining the voltage of said record medium at a reference value, a source of voltage pulses, second means for coupling said source to alternate of said nozzles, an electrical inverting circuit, and third means coupling said source through said inverting circuit to the nozzles intermediate said alternate nozzles. 